A number of photochromic materials are used in many industrial fields. The absorption spectra and thus the color of photochromic materials can change as a result of the absorption of electromagnetic radiation (e.g., visible or UV light).
Many photochromic materials possess color change properties due to the phenomenon of photochromism. Photochromism refers to a reversible, light-induced transformation of a chemical compound between at least two forms. The at least two forms inherently have different absorption spectra, so they exhibit different colors. A photochromic dye is a photochromic material exhibiting light-dependent color change properties. Absorption of light radiation can reversibly transform a photochromic dye between two forms having different absorption spectra, so as to exhibit different colors.